Shock absorbing rear suspensions for bicycles are known. In general, however, these have not proven entirely satisfactory in practice.
In most rear suspension assemblies, the rear axle pivots about a single point when subjected to bump forces, as when traversing rough terrain. In these designs, the pedaling forces which are extended by the rider tend to either compress or extend the spring/damper assembly of the rear suspension. In this respect, the spring/damper assembly of the rear suspension is affected by the pedal force and some of the rider's energy is needlessly wasted.
This effect manifests itself by the common tendency of rear suspension systems to either lock up or “squat” when the rider pedals. Since most of these systems have a single lever arm which pivots about a single axis, the lock up or squat generally occurs as a result of chain tension action on the single lever arm. If the single pivot line is above the chain line, the suspension will typically lock up and/or “jack”, thereby providing compliance only when the shock or bump force exceeds the chain tension. Conversely, if the single pivot point of the suspension system is below the chain line, the system will typically squat, since the chain tension is acting to compress the spring/damper assembly of the rear suspension system, similar to a shock or bump force.